Body-worn vital sign monitor

ABSTRACT

The invention provides a body-worn monitor featuring a processing system that receives a digital data stream from an ECG system. A cable houses the ECG system at one terminal end, and plugs into the processing system, which is worn on the patient&#39;s wrist like a conventional wristwatch. The ECG system features: i) a connecting portion connected to multiple electrodes worn by the patient; ii) a differential amplifier that receives electrical signals from each electrode and process them to generate an analog ECG waveform; iii) an analog-to-digital converter that converts the analog ECG waveform into a digital ECG waveform; and iv) a transceiver that transmits a digital data stream representing the digital ECG waveform (or information calculated from the waveform) through the cable and to the processing system. Different ECG systems, typically featuring three, five, or twelve electrodes, can be interchanged with one another.

CROSS REFERENCES TO RELATED APPLICATIONS

Not Applicable

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to medical devices for monitoring vitalsigns, e.g., arterial blood pressure.

Description of the Related Art

Conventional vital sign monitors are used throughout the hospital, andare particularly commonplace in high-acuity areas such as the intensivecare unit (ICU), emergency department (ED), or operating room (OR).Patients in these areas are generally sick and require a relatively highdegree of medical attention. The ratio between medical professionals andpatients in these areas is typically high compared to lower-acuity areasof the hospital. Even in such areas, however, it is still commonpractice for medical professionals to measure vital signs such as bloodpressure, respiratory rate, oxygen saturation (SpO2), heart rate, andtemperature. Monitoring of these parameters is typically done withportable or wall-mounted vital sign monitors. It can be difficult toeffectively monitor patients in this way, however, because they areoften ambulatory and not constrained to a single hospital room. Thisposes a problem for conventional vital sign monitors, which aretypically heavy and unwieldy, as they are not intended for theambulatory population. Some companies have developed ambulatory vitalsign monitors with limited capabilities (e.g. cuff-based blood pressureusing oscillometry and SpO2 monitoring), but typically these devicesonly make intermittent, rather than continuous, measurements. And eventhese measurements tend to work best on stationary patients, as they areeasily corrupted by motion-related artifacts.

Blood pressure is a vital sign often considered to be a good indicatorof a patient's health. In critical care environments like the ICU andOR, blood pressure can be continuously monitored with an arterialcatheter inserted in the patient's radial or femoral artery.Alternatively, blood pressure can be measured intermittently with a cuffusing oscillometry, or manually by a medical professional usingauscultation. Most vital sign monitors perform both the catheter andcuff-based measurements of blood pressure. Blood pressure can also bemonitored continuously with a technique called pulse transit time (PTT),defined as the transit time for a pressure pulse launched by a heartbeatin a patient's arterial system. PTT has been shown in a number ofstudies to correlate to systolic (SYS), diastolic (DIA), and mean (MAP)blood pressures. In these studies, PTT is typically measured with aconventional vital signs monitor that includes separate modules todetermine both an electrocardiogram (ECG) and SpO2. During a PTTmeasurement, multiple electrodes typically attach to a patient's chestto determine a time-dependent ECG component characterized by a sharpspike called the ‘QRS complex’. The QRS complex indicates an initialdepolarization of ventricles within the heart and, informally, marks thebeginning of the heartbeat and a pressure pulse that follows.

SpO2 is typically measured with a bandage or clothespin-shaped sensorthat clips to a patient's finger and includes optical systems operatingin both the red and infrared spectral regions. A photodetector measuresradiation emitted from the optical systems that transmits through thepatient's finger. Other body sites, e.g., the ear, forehead, and nose,can also be used in place of the finger. During a measurement, amicroprocessor analyses both red and infrared radiation detected by thephotodetector to determine the patient's blood oxygen saturation leveland a time-dependent waveform called a photoplethysmograph (PPG).Time-dependent features of the PPG indicate both pulse rate and avolumetric absorbance change in an underlying artery caused by thepropagating pressure pulse.

Typical PTT measurements determine the time separating a maximum pointon the QRS complex (indicating the peak of ventricular depolarization)and a foot of the PPG waveform (indicating the beginning the pressurepulse). PTT depends primarily on arterial compliance, the propagationdistance of the pressure pulse (which is closely approximated by thepatient's arm length), and blood pressure. To account forpatient-dependent properties, such as arterial compliance, PTT-basedmeasurements of blood pressure are typically ‘calibrated’ using aconventional blood pressure cuff and oscillometry. Typically during thecalibration process the blood pressure cuff is applied to the patient,used to make one or more blood pressure measurements, and then left forfuture measurements. Going forward, the calibration measurements areused, along with a change in PTT, to continuously measure the patient'sblood pressure (defined herein as ‘cNIBP’). PTT typically relatesinversely to blood pressure, i.e., a decrease in PTT indicates anincrease in blood pressure.

A number of issued U.S. patents describe the relationship between PTTand blood pressure. For example, U.S. Pat. Nos. 5,316,008; 5,857,975;5,865,755; and 5,649,543 each describe an apparatus that includesconventional sensors that measure an ECG and PPG, which are thenprocessed to determine PTT. U.S. Pat. No. 5,964,701 describes afinger-ring sensor that includes an optical system for detecting a PPG,and an accelerometer for detecting motion.

SUMMARY OF THE INVENTION

To improve the safety of hospitalized patients, particularly those inlower-acuity areas, it is desirable to have a body-worn monitor thatcontinuously measures a plurality of vital signs from a patient, andwirelessly transmits these directly to a nurse or to a central nursingstation. Preferably the monitor operates algorithms featuring: 1) a lowpercentage of false positive alarms/alerts; and 2) a high percentage oftrue positive alarms/alerts. The term ‘alarm/alert’, as used herein,refers to an audio and/or visual alarm generated directly by a monitorworn on the patient's body, or alternatively a remote monitor (e.g., acentral nursing station). To accomplish this, the invention provides abody-worn monitor that measures a patient's vital signs (e.g. bloodpressure, SpO2, heart rate, respiratory rate, and temperature) whilesimultaneously characterizing their activity state (e.g. resting,walking, convulsing, falling) and posture (upright, supine). Thebody-worn monitor processes this information to minimize corruption ofthe vital signs and associated alarms/alerts by motion-relatedartifacts.

The body-worn monitor can include a software framework that generatesalarms/alerts based on threshold values that are either preset ordetermined in real time. The framework additionally includes a series of‘heuristic’ rules that take the patient's activity state and motion intoaccount, and process the vital signs accordingly. These rules, forexample, indicate that a walking patient is likely breathing and has aregular heart rate, even if their motion-corrupted vital signs suggestotherwise.

The body-worn monitor features a series of sensors that attach to thepatient to measure time-dependent PPG, ECG, accelerometer-based motion(ACC), oscillometric (OSC), respiratory rate (RR), and impedancepneumography (IP) waveforms. A microprocessor (CPU) within the monitorcontinuously processes these waveforms to determine the patient's vitalsigns, degree of motion, posture and activity level. Sensors thatmeasure these signals typically send digitized information to awrist-worn transceiver through a serial interface, or bus, operating ona controlled area network (CAN) protocol. The CAN bus is typically usedin the automotive industry, which allows different electronic systems toeffectively and robustly communicate with each other with a small numberof dropped packets, even in the presence of electrically noisyenvironments. This is particularly advantageous for ambulatory patientsthat may generate signals with large amounts of motion-induced noise.

Blood pressure, a vital sign that is particularly useful forcharacterizing a patient's condition, is typically calculated from a PTTvalue determined from the PPG and ECG waveforms. Once determined, bloodpressure and other vital signs can be further processed, typically witha server within a hospital, to alert a medical professional if thepatient begins to decompensate.

In other embodiments, PTT can be calculated from time-dependentwaveforms other than the ECG and PPG, and then processed to determineblood pressure. In general, PTT can be calculated by measuring atemporal separation between features in two or more time-dependentwaveforms measured from the human body. For example, PTT can becalculated from two separate PPGs measured by different optical sensorsdisposed on the patient's fingers, wrist, arm, chest, or virtually anyother location where an optical signal can be measured using atransmission or reflection-mode optical configuration. In otherembodiments, PTT can be calculated using at least one time-dependentwaveform measured with an acoustic sensor, typically disposed on thepatient's chest. Or it can be calculated using at least onetime-dependent waveform measured using a pressure sensor, typicallydisposed on the patient's bicep, wrist, or finger. The pressure sensorcan include, for example, a pressure transducer, piezoelectric sensor,actuator, polymer material, or inflatable cuff.

In one aspect, the invention provides a body-worn monitor featuring aprocessing system that receives a digital data stream from an ECGsystem. A cable houses the ECG system at one terminal end, and plugsinto the processing system, which is typically worn on the patient'swrist like a conventional wristwatch. Specifically, the ECG systemfeatures: i) a connecting portion connected to multiple electrodes wornby the patient; ii) a differential amplifier that receives electricalsignals from each electrode and process them to generate an analog ECGwaveform; iii) an analog-to-digital converter that converts the analogECG waveform into a digital ECG waveform; and iv) a transceiver thattransmits a digital data stream representing the digital ECG waveform(or information calculated from the waveform) through the cable and tothe processing system. Different ECG systems, preferably featuringthree, five, or twelve electrodes, can be interchanged with one another.

In embodiments, the ECG system features a single-chip solution fordetermining ECG and IP waveforms, heart rate, respiratory rate, errorcodes, and diagnostic information such as ventricular tachycardia(VTAC), ventricular fibrillation (VFIB), and premature ventricularcontractions (PVCs). A mechanical housing enclosing the ECG system canadditionally house a motion-detecting sensor (e.g. a three-axis digitalaccelerometer) and a temperature sensor (e.g. a thermocouple). The cablefeatures at least one conductor (and typically two conductors) thattransmits both a first digital data stream representing the digital ECGwaveform and a second digital data stream representing a digital motionwaveform (e.g. an ACC waveform) generated by the accelerometer. Bothdigital data streams typically include a header portion indicating thesource of the data stream, and a data portion that includes any relevantinformation. For the ECG system, such information includes an ECGwaveform, heart rate, an error code, and a physiological statecorresponding to the patient (e.g. VTAC, VFIB, PVCs). The data portioncorresponding to the accelerometer includes information such as the ACCwaveform, degree of motion, posture, and an activity level correspondingto the patient.

In another aspect, the system described above also features anoscillometry system that includes: i) a cuff, typically worn on thepatient's arm to apply a pressure; ii) a pneumatic system that inflatesthe cuff and detects pressure therein to generate an analogoscillometric waveform; iii) an analog-to-digital converter thatconverts the analog oscillometric waveform into a digital oscillometricwaveform; iv) a transceiver component that transmits a digitaloscillometric data stream representing the digital oscillometricwaveform (or values calculated therefrom) through a second serial portand to the processing system. In this case the digital oscillometry datastream features a header portion that indicates the origin of thepacket, and a data portion that includes information such as a pressurewaveform, blood pressure, heart rate, error codes, and a physiologicalstate corresponding to the patient.

The system can also connect through one of its serial ports to anancillary third system that can be, for example, a system that deliversa compound or other therapeutic intervention to the patient, or that cangather other data from the patient. Such systems include infusion pumps,insulin pumps, hemodialysis machines, glucometers, and systems fordelivering oxygen, such as a mechanical ventilator. This list is notmeant to be limiting. In the case of a therapeutic compound, the dataportion of the packet can indicate the type of compound delivered to thepatient, a dosage of the compound, and a rate of delivery of thecompound. The third system can also be a sensor configured to measure asignal from the patient. Such sensors include, for example, a pulseoximeter, EEG monitor, temperature sensor, respiratory rate sensor,motion sensor, camera, impedance plethysmography sensor, opticalspectrometer, and skin-conductance sensor. Again, this list is not meantto be limiting. Here, the data portion of the packet can includewaveform information, heart rate, pulse rate, SpO2 value, EEG waveform,temperature, respiratory rate, degree of motion, posture, activitylevel, arm height, an image, a property of the patient measurableoptically, and a property of the patient measurable electrically.

In embodiments, both the ECG and oscillometry systems include separatemicroprocessors, both of which are in communication with the processingsystem within the wrist-worn transceiver. For example, the processingsystem can send a packet (containing, e.g., a timing parameter) to themicroprocessor within the ECG and oscillometry systems to synchronizethem with the processing system worn on the wrist.

Preferably the transceiver component used in each of the above-describedsystems is a serial transceiver operating the Controller Area Network(“CAN”) protocol. CAN is a multi-master broadcast serial bus standardfor connecting electronic control units (ECUs). Each node is able tosend and receive messages, but not simultaneously; a message, consistingprimarily of an ID (usually chosen to identify the message-type/sender)and (up to eight) message bytes, is transmitted onto the bus and issensed by all nodes. CAN transceivers associated with the ECG andpneumatic systems need to be synchronized to prevent any significantdrift that may occur between the different time-domain waveforms theygenerate. This is typically done using a series of timing packets,described in detail below, that are sent between the wrist-worntransceiver and these remote systems.

In another aspect, the system provides a method for calculating bloodpressure from a patient that features the following steps: (a)generating a first digital waveform indicating an ECG signal with afirst remote sensor; (b) generating a second digital waveform indicatinga pressure signal with a second remote sensor; (c) generating an analogwaveform indicating an optical signal with a third remote sensor; (d)synchronizing the first digital waveform, the second digital waveform,and a digitized version of the analog waveform; (e) determining a pulsetransit time from the first digital waveform and a digitized version ofthe analog waveform; (f) determining a calibration from the firstdigital waveform, the second digital waveform, and a digitized versionof the analog waveform; and (g) determining a blood pressure value fromthe calibration and a pulse transit time.

Typically the optical signal is generated with an optical sensorconfigured to be worn around the patient's thumb. PTT is typicallycalculated from a time difference separating a QRS complex in the ECGwaveform and a foot of a PPG waveform. In other embodiments the sameoptical sensor used to measure the optical waveform features a first LEDoperating in the red spectral range, and a second LED operating in theinfrared spectral range. Optical waveforms measured with these LEDs canadditionally be processed to determine SpO2, as is described in detailbelow.

The pressure signal is typically generated with a cuff-based pneumaticsystem wrapped around the patient's arm, and is typically measuredduring an inflation-based oscillometry measurement. Here, the processingcomponent in the wrist-worn transceiver is further configured tocalculate a calibration from a group of pulse transit times, whereineach pulse transit time in the group is measured when a differentpressure is applied to the patient's arm. These data are then processedwith a model that estimates an ‘effective’ blood pressure in thepatient's arm during the inflation-based measurement, and uses this toestimate a relationship between PTT and blood pressure for the patient.This relationship represents a calibration that is then used withfollow-on PTT measurements to measure the patient's cNIBP.

In another aspect, the invention provides a body-worn vital sign monitorfeaturing a processing component that includes a system for detecting anidentifying code from a medical professional, and in response renderinga specific graphical user interface (GUI) on the wrist-worn transceiver.Preferably the system for detecting an identifying code is a barcodescanner, and the identifying code is a barcode printed on, e.g., thebadge of the medical professional. Alternatively, a system based onradio-frequency identifying codes (RFID) is used in place of the barcodescanner. In still other embodiments the identifying code is simply analphanumeric password entered into a GUI on the transceiver by themedical professional. In all cases, the identifying code prompts thetransceiver to render a GUI that is appropriate for the medicalprofessional, but not necessarily for the patient. Such a GUI mayinclude, for example, time-domain waveforms, vital sign information, andparameters relating to alarms/alerts. The GUI for the patient istypically much simpler, and includes information such as the time of dayand a ‘nurse call’ button. To support this feature, the wrist-worntransceiver typically includes a speaker and system for communicatingover the hospital's wireless network using standard voice over IP (VoIP)protocols. The speaker can also play pre-recorded messages that may begermane to the patient.

The GUI displayed by the wrist-worn transceiver may depend on theorientation of the transceiver. This can be determined, for example, bysignals generated by an internal accelerometer. For example, when thetransceiver is oriented to face a medical professional, theaccelerometer can generate representative signals that can be processedby an internal CPU, which in response will render a GUI suitable for themedical professional. Alternatively, the CPU will render a GUI suitablefor the patient when signals from the accelerometer indicate that thetransceiver is oriented towards the patient.

The wrist-worn transceiver can communicate with a remote device througha wireless connection that operates on the hospital's wireless network,or alternatively through a peer-to-peer connection. In another aspect ofthe invention, for example, the remote device is configured tosimultaneously display vital signs for each patient in a group when asignal strength corresponding to each wrist-worn transceiver in thegroup is below a pre-determined threshold value. When the signalstrength from the wireless system worn by a patient exceeds thepre-determine threshold, the remote monitor displays information forthat particular patient. Such a situation would occur, for example, if atablet computer normally disposed at a central nursing station wasbrought into the patient's room. Typically the pre-determined thresholdvalue is between about −100 and −80 dB, and the wireless system used byeach wrist-worn transceiver operates on an industry-standardcommunications protocol, preferably selected from 802.11, 802.15.4, andcellular wireless protocols. In embodiments, the remote device is adevice comprising a microprocessor, a display, and a compatiblecommunications transceiver. Examples include a computing device selectedfrom the group consisting of a desktop computer, a portable computer, atablet computer, a cellular telephone, and a personal digital assistant.This list is not meant to be limiting.

In yet another aspect, the invention provides a body-worn monitorfeaturing a ‘hot swappable’ battery. Here, the transceiver operates analgorithm that performs the following steps: (b) display on a GUI thatthe battery needs to be replaced; (c) detect when a secondary device isplugged into one of the serial ports, the secondary device indicatingthat the battery is about to be replaced; (d) store settingscorresponding to the wireless system (e.g. IP and/or MAC addresses,passwords, encryption keys) and the patient's vital signs in thenon-volatile memory; and (e) indicate on the GUI that the battery can bereplaced. Once this is done, the depleted battery is replaced with a newone, and a button on the GUI is pressed to resume a wireless connectionto the hospital's network. Continuous monitoring of the patient resumesonce this is complete. Typically the secondary device plugs into aserial port on the transceiver, and sends a serial packet over the CANbus indicating the battery is ready to be swapped.

The body-worn monitor can determine a patient's location in addition totheir vital signs and motion-related properties. Typically, thelocation-determining sensor and the wireless transceiver operate on anindustry-standard communications system, e.g. a wireless system based on802.11, 802.15.4, or cellular protocols. In this case a location isdetermined by processing the wireless signal with one or more algorithmsknown in the art. These include, for example, triangulating signalsreceived from at least three different wireless base stations, or simplyestimating a location based on signal strength and proximity to aparticular base station. In still other embodiments the location sensorincludes a conventional global positioning system (GPS).

The body-worn monitor can include a first voice interface, and theremote computer can include a second voice interface that integrateswith the first voice interface. The location sensor, wirelesstransceiver, and first and second voice interfaces can all operate on acommon wireless system, such as one of the above-described systems basedon 802.11 or cellular protocols. The remote computer, for example, canbe a monitor that is essentially identical to the monitor worn by thepatient, and can be carried or worn by a medical professional. In thiscase the monitor associated with the medical professional features adisplay wherein the user can select to display information (e.g. vitalsigns, location, and alarms) corresponding to a particular patient. Thismonitor can also include a voice interface so the medical professionalcan communicate with the patient.

Blood pressure is determined continuously and non-invasively using atechnique, based on PTT, which does not require any source for externalcalibration. This technique, referred to herein as the ‘CompositeTechnique’, determines blood pressure using PPG, ECG, and OSC waveforms.The Composite Technique is described in detail in the co-pending patentapplication, the contents of which are fully incorporated herein byreference: VITAL SIGN M FOR MEASURING BLOOD PRESSURE USING OPTICAL,ELECTRICAL, AND PRESSURE WAVEFORMS (U.S. Ser. No. 12/1q38, 194; filedJun. 12, 2008).

Still other embodiments are found in the following detailed descriptionof the invention, and in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic drawing of a body-worn monitor featuringsensors for measuring ECG, PPG, ACC, OSC, and RR waveforms, and systemsfor processing these to determine a patient's vital signs;

FIG. 2 shows a schematic drawing of a patient wearing the body-wornmonitor of FIG. 1 and its associated sensors;

FIG. 3 is a graph of time-dependent ECG, PPG, OSC, ACC, and RR waveformsgenerated with the body-worn monitor and sensors of FIG. 2;

FIGS. 4A and 4B show three-dimensional images of the body-worn monitorof FIG. 1 attached to a patient with and without, respectively, acuff-based pneumatic system used for a calibrating indexing measurement;

FIGS. 5A and 5B show, respectively, three-dimensional images of thewrist-worn transceiver before and after receiving cables from othersensors within the body-worn monitor;

FIG. 5C shows a top view of the wrist-worn transceiver of FIGS. 5A and5B rendering a GUI;

FIGS. 6A, 6B, 6C and 6D show, respectfully, side (6A, C) and top (6B, D)views of the wrist-worn transceiver of FIGS. 5A-C before, during, andafter a battery hot swap;

FIG. 7A shows a three-dimensional image of the body-worn monitor of FIG.4B attached to a patient along with the ECG system;

FIG. 7B shows a schematic drawing of the ECG system within the body-wornmonitoring of FIG. 7A;

FIG. 8A shows a three-dimensional image of the body-worn monitor of FIG.4B attached to a patient along with the cuff-based pneumatic system;

FIGS. 8B and 8C show, respectively, side and three-dimensional views ofthe pneumatic components with the cuff-based pneumatic system of FIG.8A;

FIG. 9A shows a three-dimensional image of the body-worn monitor of FIG.4B attached to a patient along with the thumb-worn optical sensor;

FIG. 9B is a schematic circuit diagram of the thumb-worn optical sensorof FIG. 9A and the switching components used to control itslight-emitting diodes (LEDs);

FIG. 10 is a schematic circuit diagram of the amplifier/filter circuitused to process signals from the thumb-worn optical sensor shown in FIG.9B;

FIG. 11 shows a schematic drawing of the ACC, ECG, pneumatic, andauxiliary systems of the body-worn monitor communicating over the CANprotocol with the wrist-worn transceiver;

FIG. 12A shows a three-dimensional view of the wrist-worn transceiver ofFIG. 5C scanning a barcode printed on a badge of a medical professional;

FIGS. 12B and 12C show, respectively, patient and medical professionalviews used in the GUI rendered on the wrist-worn transceiver of FIG.12A;

FIG. 13 shows a series of icons used to indicate the patient's postureand activity level in the GUI shown in FIGS. 12C, 15A, and 15B;

FIG. 14 shows a three-dimensional view of the wrist-worn transceiver ofFIG. 5C interfacing with a tablet computer and personal digitalassistant (PDA) through, respectively, network and peer-to-peer wirelesscommunication protocols;

FIGS. 15A and 15B show, respectively, patient and map views used in theGUI rendered on the remote tablet computer of FIG. 14; and

FIG. 16 is a schematic drawing showing a sequence of pressure-dependentand pressure-free measurements made according to the Composite Techniqueusing the body-worn monitor of FIGS. 4A and 4B.

DETAILED DESCRIPTION OF THE INVENTION System Overview

FIG. 1 shows a schematic drawing of a body-worn monitor 10 according tothe invention featuring a wrist-worn transceiver 72 that continuouslydetermines vital signs (e.g. blood pressure, SpO2, heart rate,respiratory rate, and temperature) and motion-related properties (e.g.posture, arm height, activity level, and degree of motion) for anambulatory patient in a hospital. The monitor 10 is small, lightweight,and comfortably worn on the patient's body during their stay in thehospital; its form factor is described in detail below. A medicalprofessional can apply the monitor, for example, to a recently admittedpatient waiting in the ED, and the same monitor can provide continuousmonitoring during their stay in the hospital. For example, the patientcan wear the monitor in their hospital room, as they receive specificprocedures or tests, during transport to other rooms, and even duringsurgery. The monitor 10 provides continuous monitoring, and features asoftware framework that determines alarms/alerts if the patient beginsto decompensate. The framework processes both the patient's motion andtheir vital sign information with algorithms that reduce the occurrenceof false alarms.

A combination of features makes the body-worn monitor 10 ideal forambulatory patients within the hospital. For example, its wrist-worntransceiver 72 features a wireless transmitter 24 that communicatesthrough a hospital network to a computer (e.g. a portable tabletcomputer) at a central nursing station 43, and to a local computer 44(e.g. a hand-held PDA) through a peer-to-peer connection. The specificmode of communication can be determined automatically (using, e.g., asignal strength associated with the wireless connection), or manuallythrough an icon on the GUI.

The transceiver 72 features a CPU 22 that communicates through a digitalCAN interface, or bus, to external systems featuring ECG 16, externalaccelerometers 14 b-c, pneumatic 20, and auxiliary 45 sensors. Eachsensor 16, 14 b-c, 20, 45 is ‘distributed’ on the patient to minimizethe bulk and weight normally associated with conventional vital signmonitors, which typically incorporate all electronics associated withmeasuring vital signs in a single plastic box. Moreover, each of thesesensors 16, 14 b-c, 20, 45 generate digital signals close to where theyactually attach to the patient, as opposed to generating an analogsignal and sending it through a relatively long cable to a central unitfor processing. This can reduce noise due to cable motion which is oftenmapped onto analog signals. Cables 40, 38, 46 used in the body-wornmonitor 10 to transmit packets over the CAN bus typically include 5separate wires bundled together with a single protective cladding: thewires supply power and ground to the remote ECG system 16,accelerometers 14 b-c, pneumatic 20, and auxiliary systems 45; providehigh/low signal transmission lines for data transmitted over the CANprotocol; and provide a grounded electrical shield for each of thesefour wires. There are several advantages to this approach. First, asingle pair of transmission lines in the cable (i.e. the high/low signaltransmission lines) can transmit multiple digital waveforms generated bycompletely different sensors. This includes multiple ECG waveforms(corresponding, e.g., to vectors associated with three, five, andtwelve-lead ECG systems) from the ECG circuit, along with ACC waveformsassociated with the x, y, and z axes of accelerometers within thebody-worn monitor 10. The same two wires, for example, can transmit upto twelve ECG waveforms (measured by a 12-lead ECG system), and six ACCwaveforms (measured by the accelerometers 14 b-c). Limiting thetransmission line to a pair of conductors reduces the number of wiresattached to the patient, thereby decreasing the weight and anycable-related clutter. Second, cable motion induced by an ambulatorypatient can change the electrical properties (e.g. electricalimpendence) of its internal wires. This, in turn, can add noise to ananalog signal and ultimately the vital sign calculated from it. Adigital signal, in contrast, is relatively immune to such motion-inducedartifacts.

The ECG 16, pneumatic 20, and auxiliary 45 systems are stand-alonesystems that include a separate CPU, analog-to-digital converter, andCAN transceiver. During a measurement, they connect to the transceiver72 through cables 40, 38, 46 and connectors 30, 28, 32 to supply digitalinputs over the CAN bus. The ECG system 16, for example, is completelyembedded in a terminal portion of its associated cable. Systems forthree, five, and twelve-lead ECG monitoring can be swapped in an outsimply by plugging the appropriate cable (which includes the ECG system16) into a CAN connector 30 on the wrist-worn transceiver 72, and theattaching associated electrodes to the patient's body.

The wrist-worn transceiver 72 renders separate GUIs that can be selectedfor a particular viewer, e.g., different displays directed to thepatient as compared to a medical professional. To do this, thetransceiver 72 includes a barcode scanner 42 that can scan anidentifying barcode printed, e.g., on the medical professional's badge,which indicates the viewer's identity or type to the system. Inresponse, the system renders a GUI featuring information (e.g. vitalsigns, waveforms) tailored for the indicated viewer; that is, a medicalprofessional can receive information on the GUI that may not be suitablefor viewing by the patient. So that the patient can communicate with themedical professional, the transceiver 72 includes a speaker 41interfaced to the CPU 22 and wireless system 24 that allows the patientto communicate with a remote medical professional using a standard VoIPprotocol. A Li:ion battery 39 powers the transceiver 72 for about fourdays on a single charge, and can be removed in a ‘hot swap’ manner sothat after the battery change the transceiver remains wirelesslyconnected to the hospital's network and no information is lost. This isdone simply by plugging a specialized ‘dongle’ into the CAN connector 32for the auxiliary system 45, replacing the battery 39, and then removingthe dongle.

Three separate digital accelerometers 14 a-c are non-obtrusivelyintegrated into the monitor's form factor; two of them 14 b-c arelocated on the patient's body, separate from the wrist-worn transceiver72, and send digitized, motion-related information through the CAN busto the CPU 22. The first accelerometer 14 a is mounted on a circuitboard within the transceiver 72, and monitors motion of the patient'swrist. The second accelerometer 14 b is incorporated directly into thecable 40 connecting the ECG system 16 to the transceiver 72 so that itcan easily attach to the patient's bicep and measure motion and positionof the patient's upper arm. As described below, this can be used tocompensate for hydrostatic forces associated with changes in thepatient's arm height that affect the monitor's blood pressuremeasurement, and can be additionally used to calibrate the monitor'sblood pressure measurement through the patient's ‘natural’ motion. Thethird accelerometer 14 c is typically mounted to a circuit board thatsupports the ECG system 16 on the terminal end of the cable, andtypically attaches to the patient's chest. Motion and position of thepatient's chest can be used to determine their posture and activitystates, which as described below can be used with vital signs forgenerating alarm/alerts. Each accelerometer 14 a-c measures three uniqueACC waveforms, each corresponding to a separate axis (x, y, or z)representing a different component of the patient's motion. To determineposture, arm height, activity level, and degree of motion, thetransceiver's CPU 22 processes signals from each accelerometer 14 a-cwith a series of algorithms, described in the following pending patentapplications, the contents of which are incorporated herein byreference: BODY-WORN MONITOR FEATURING ALARM SYSTEM THAT PROCESSES APATIENT'S MOTION AND VITAL SIGNS (U.S. Ser. No. 12/469,182; filed May20, 2009) and BODY-WORN VITAL SIGN MONITOR WITH SYSTEM FOR DETECTING ANDANALYZING MOTION (U.S. Ser. No. 12/469,094; filed May 20, 2009). Intotal, the CPU 22 can process nine unique, time-dependent signals(ACC₁₋₉) corresponding to the three axes measured by the three separateaccelerometers. Algorithms determine parameters such as the patient'sposture (e.g., sitting, standing, walking, resting, convulsing,falling), the degree of motion, the specific orientation of thepatient's arm and how this affects vital signs (particularly bloodpressure), and whether or not time-dependent signals measured by the ECG16, optical 18, or pneumatic 20 systems are corrupted by motion.

To determine blood pressure, the transceiver 72 processes ECG and PPGwaveforms measured, respectively, by the ECG 16 and optical 18 systems.The optical system 18 features a thumb-worn sensor that includes LEDsoperating in the red (λ˜660 nm) and infrared (λ˜900 nm) spectralregions, and a photodetector that detects their radiation after itpasses through arteries within the patient's thumb. The ECG waveform, asdescribed above, is digitized and sent over the CAN interface to thewrist-worn transceiver 72, while the PPG waveform is transmitted in ananalog form and digitized by an analog-to-digital converter within thetransceiver's circuit board. The pneumatic system 20 provides adigitized pressure waveform and oscillometric blood pressuremeasurements (SYS, DIA, and MAP) through the CAN interface; these areprocessed by the CPU 22 to make cuff-based ‘indexing’ blood pressuremeasurements according to the Composite Technique. The indexingmeasurement typically only takes about 40-60 seconds, after which thepneumatic system 20 is unplugged from its connector 28 so that thepatient can move within the hospital without wearing an uncomfortablecuff-based system.

Collectively, these systems 14 a-c, 16, 18, and 20 continuously measurethe patient's vital signs and motion, and supply information to thesoftware framework that calculates alarms/alerts. A third connector 32also supports the CAN bus and is used for auxiliary medical devices(e.g. a glucometer, infusion pump, system for end-tidal CO2) that iseither worn by the patient or present in their hospital room.

Once a measurement is complete, the transceiver 72 uses an internalwireless transmitter 24 to send information in a series of packets to aremote monitor 43, 44 within the hospital. The wireless transmitter 24typically operates on a protocol based on 802.11, and can communicatewith a computer located at a central nursing station 43 through anexisting network within the hospital, or through a peer-to-peerconnection to a local computer or display 44 (e.g. a PDA worn by amedical professional). Information transmitted by the transceiver alertsthe medical professional if the patient begins to decompensate. A serverconnected to the hospital network typically generates this alarm/alertonce it receives the patient's vital signs, motion parameters, ECG, PPG,and ACC waveforms, and information describing their posture, andcompares these parameters to preprogrammed threshold values. Asdescribed in detail below, this information, particularly vital signsand motion parameters, is closely coupled together. Alarm conditionscorresponding to mobile and stationary patients are typically different,as motion can corrupt the accuracy of vital signs (e.g., by addingnoise), and induce artificial changes in them (e.g., throughacceleration of the patient's heart and respiratory rates) that may notbe representative of the patient's actual physiology.

Measuring Time-Dependent Physiological Signals with the Body-WornMonitor

FIGS. 2 and 3 show how a network of sensors 78 a-c, 83, 84, 87, 94within the body-worn monitor 10 connect to a patient 70 to characterizethem within a hospital. During a measurement, the sensors 78 a-c, 83,84, 87, 94 measure signals that are processed by the monitor 10 togenerate time-dependent ECG 61, PPG 62, OSC 63, ACC 64, and RR 65waveforms. These, in turn, yield the patient's vital signs and motionparameters. Each waveform 61-65 relates to a unique physiologicalcharacteristic of the patient 70. For example, each of the patient'sheartbeats generates electrical impulses that pass through the body nearthe speed of light, along with a pressure wave that propagates throughthe patient's vasculature at a significantly slower speed. Immediatelyafter the heartbeat, the pressure wave leaves the heart 148 and aorta149, passes through the subclavian artery 150 to the brachial artery144, and from there through the radial and ulnar arteries 145 to smallerarteries in the patient's fingers. Three disposable electrodes 78 a-cattached to the patient's chest measure unique electrical signals whichpass to a single-chip ECG circuit 83 that terminates a distal end of theECG cable. Typically, these electrodes attach to the patient's chest ina conventional ‘Einthoven's triangle’ configuration featuring threeunique ‘vectors’, each corresponding to a different lead (e.g. LEAD I,II, II). Related configurations can also be used when five andtwelve-lead ECG systems are used in place of the three-lead system, asdescribed below with reference to FIGS. 7A,B. Within the ECG circuit 83signals are processed using an amplifier/filter circuit andanalog-to-digital converter to generate a digital ECG waveform 61corresponding to each lead. The ECG waveform 61 features a sharp,well-defined QRS complex corresponding to each heartbeat; this marks theinitiation of the patient's cardiac cycle. Heart rate is determineddirectly from the ECG waveform 61 using known algorithms, such as thosedescribed in the following reference, the contents of which areincorporated herein by reference: ‘ECG Beat Detection Using FilterBanks’, Afonso et al., IEEE Trans. Biomed Eng., 46:192-202 (1999).

To generate an IP waveform, one of the ECG electrodes in the circuit 78a is a ‘driven lead’ that injects a small amount of modulated currentinto the patient. A second, non-driven electrode 78 c, typically locatedon the opposite side of the torso, detects the current, which is furthermodulated by capacitance changes in the patient's chest cavity resultingfrom breathing. Further processing and filtering of the IP waveformsyields an oscillating RR waveform 65 which can be further processed tocalculate respiratory rate.

The optical sensor 94, described in detail with reference to FIGS. 9A,B,features two LEDs and a single photodetector that collectively measure atime-dependent PPG waveform 62 corresponding to each of the LEDs. Thesensor and algorithms for processing the PPG waveforms are described indetail in the following co-pending patent application, the contents ofwhich are fully incorporated herein by reference: BODY-WORN PULSEOXIMETER (U.S. Ser. No. 61/218,062; filed Jun. 17, 2009). The waveform62 represents a time-dependent volumetric change in vasculature (e.g.arteries and capillaries) that is irradiated with the sensor's opticalcomponents. Volumetric changes are induced by a pressure pulse launchedby each heartbeat that travels from the heart 148 to arteries andcapillaries in the thumb according to the above-describe arterialpathway. Pressure from the pressure pulse forces a bolus of blood intothis vasculature, causing it to expand and increase the amount ofradiation absorbed, and decrease the transmitted radiation at thephotodetector. The pulse shown in the PPG waveform 62 thereforerepresents the inverse of the actual radiation detected at thephotodetector. It follows the QRS complex in the ECG waveform 61,typically by about one to two hundred milliseconds. The temporaldifference between the peak of the QRS complex and the foot of the pulsein the PPG waveform 62 is the PTT, which as described in detail below isused to determine blood pressure according to the Composite Technique.PPG waveforms generated by both the red and infrared LEDs are alsoprocessed by the CPU within the wrist-worn transceiver to determineSpO2, as is described in detail in the above-mentioned patentapplication. PTT-based measurements made from the thumb yield excellentcorrelation to blood pressure measured with a femoral arterial line.This provides an accurate representation of blood pressure in thecentral regions of the patient's body.

Each accelerometer generates three time-dependent ACC waveforms 64,corresponding to the x, y, and z-axes, which collectively, indicate thepatient's motion, posture, and activity level. The body-worn monitor, asdescribed above, features three accelerometers that attach to thepatient: one in the wrist-worn transceiver 72, one in the ECG circuit83, and one near the bicep 87 that is included in the cable connectingthese two components. The frequency and magnitude of change in the shapeof the ACC waveform 64 indicate the type of motion that the patient isundergoing. For example, the waveform 64 can feature a relativelytime-invariant component indicating a period of time when the patient isrelatively still, and a time-variant component when the patient'sactivity level increases. Magnitudes of both components will depend onthe relationship between the accelerometer and a gravity vector, and cantherefore be processed to determine time-invariant features, such asposture and arm height. A frequency-dependent analysis of thetime-variant components yields the type and degree of patient motion.Analysis of ACC waveforms 64 is described in detail in theabove-mentioned patent applications, the contents of which have beenfully incorporated herein by reference.

The OSC waveform 63 is generated from the patient's brachial artery 144with the pneumatic system and a cuff-based sensor 84 during thepressure-dependent portion of the Composite Technique. It represents atime-dependent pressure, measured during inflation, which is applied tothe brachial artery and measured by a digital pressure sensor within thepneumatic system. The waveform 63 is similar to waveforms measuredduring deflation by conventional oscillometric blood pressure monitors.For the Composite Technique, however, the waveform 63 is typicallymeasured as the cuff gradually inflates, as is described in detail inthe following patent application, the contents of which have beenpreviously incorporated herein by reference: VITAL SIGN MONITOR FORMEASURING BLOOD PRESSURE USING OPTICAL, ELECTRICAL, AND PRESSUREWAVEFORMS (U.S. Ser. No. 12/138,194; filed Jun. 12, 2008).

During a measurement, the pressure waveform 63 increases in a mostlylinear fashion as pressure applied by the cuff 84 to the brachial artery144 increases. When it reaches a pressure slightly below the patient'sdiastolic pressure, the brachial artery 144 begins to compress,resulting in a series time-dependent pulsations caused by each heartbeatthat couple into the cuff 84. The pulsations modulate the OSC waveform63 with an amplitude that varies in a Gaussian-like distribution, withmaximum modulation occurring when the applied pressure is equivalent tothe patient's MAP. The pulsations can be filtered out and processedusing digital filtering techniques, such as a digital bandpass filterthat passes frequencies ranging from 0.5-20 Hz. The resulting waveformcan be processed to determine SYS, DIA, and MAP, as is described indetail in the above-referenced patent application, the contents of whichhave been previously incorporated herein by reference. The cuff 84 andpneumatic system are removed from the patient's bicep once thepressure-dependent component of the Composite Technique is complete.

The high-frequency component of the OSC waveform 63 (i.e. the pulses)can be filtered out to estimate the exact pressure applied to thepatient's brachial artery during oscillometry. According to theComposite Technique, PTT measured while pressure is applied willgradually increase as the brachial artery is occluded and blood flow isgradually reduced. The pressure-dependent increase in PTT can be fitwith a model to estimate the patient-specific relationship between PTTand blood pressure. This relationship, along with SYS, MAP, and DIAdetermined from the OSC waveform during inflation-based oscillometry, isused during the Composite Technique's pressure-free measurements todetermine blood pressure directly from PTT.

There are several advantages to making the indexing measurement duringinflation, as opposed to deflation. Measurements made during inflationare relatively fast and comfortable compared to those made duringdeflation. Inflation-based measurements are possible because of theComposite Technique's relatively slow inflation speed (typically 5-10mmHg/second) and the high sensitivity of the pressure sensor used withinthe body sensor. Such a slow inflation speed can be accomplished with asmall pump that is relatively lightweight and power efficient. Moreover,measurements made during inflation can be immediately terminated oncesystolic blood pressure is calculated. This tends to be more comfortablethan conventional cuff-based measurements made during deflation. In thiscase, the cuff typically applies a pressure that far exceeds thepatient's systolic blood pressure; pressure within the cuff then slowlybleeds down below the diastolic pressure to complete the measurement.

A digital temperature sensor proximal to the ECG circuit 83 measures thepatient's skin temperature at their torso. This temperature is anapproximation of the patient's core temperature, and is used mostly forpurposes related to trending and alarms/alerts.

Hardware System for Body-Worn Monitor

FIGS. 4A and 4B shows the specific form factor of the exemplarybody-worn monitor 10 described in FIGS. 1 and 2, and how the monitor 10attaches to a patient 70. Two configurations of the system are shownwith these figures: FIG. 4A shows the system used during thepressure-dependent indexing portion of the Composite Technique, andincludes a pneumatic, cuff-based system 85 attached to the patient'sbicep; FIG. 4B shows the system used for subsequent SpO2 and cNIBPmeasurements, which rely solely on PTT. The indexing measurementtypically takes about 60 seconds, and is typically performed once at thebeginning of a measurement, and every 4-8 hours afterwards. Once theindexing measurement is complete the cuff-based system 85 is typicallyremoved from the patient. The remainder of the time the monitor 10measures other vital signs and cNIBP according to the CompositeTechnique.

The body-worn monitor 10 features a wrist-worn transceiver 72 with atouch panel interface 73 that displays numerical values for all thevital signs. A wrist strap 90 affixes the transceiver 72 to thepatient's wrist like a conventional wristwatch. A five-wire cable 92connects the transceiver 72 to an optical sensor 94 that wraps aroundthe base of the patient's thumb. During a measurement, the opticalsensor 94 generates a time-dependent PPG which is processed along withan ECG to measure cNIBP and SpO2, as described above.

To determine ACC waveforms the body-worn monitor 10 features threeseparate accelerometers located at different portions on the patient'sarm and chest. The first accelerometer is surface-mounted on a circuitboard in the wrist-worn transceiver 72 and measures signals associatedwith movement of the patient's wrist. As described above, this motioncan also be indicative of that originating from the patient's fingers,which will affect both the SpO2 and cNIBP measurements. The secondaccelerometer is included in a small bulkhead portion 96 included alongthe span of the cable 82. During a measurement, a small piece ofdisposable tape, similar in size and shape to a conventional bandaid,affixes the bulkhead portion 96 to the patient's arm. In this way thebulkhead portion 96 serves two purposes: 1) it measures a time-dependentACC waveform from the mid-portion of the patient's arm, thereby allowingtheir posture and arm height to be determined as described above; and 2)it secures the cable 82 to the patient's arm to increase comfort andperformance of the body-worn monitor 10, particularly when the patientis ambulatory.

The cuff-based module 85 features a pneumatic system 76 that includes apump, manifold, two solenoid valves, pressure fittings, pressure sensor,analog-to-digital converter, microcontroller, and rechargeable Li:ionbattery. These components are described in more detail with reference toFIG. 8A-C. During an indexing measurement, the pneumatic system 76inflates a disposable cuff 84 and performs the indexing measurementaccording to the Composite Technique, described above. The cuff 84attached to the pneumatic system 76 is typically disposable and featuresan internal, airtight bladder that wraps around the patient's bicep todeliver a uniform pressure field. A pneumatic fitting on the cuff'souter surface snaps into a pressure fitting so that the pneumatic systemsits flat against the cuff to simplify application and make the systemas low-profile as possible. During the indexing measurement, pressurevalues are digitized by the internal analog-to-digital converter, andsent through a cable 86 according to the CAN protocol, along with SYS,DIA, and MAP blood pressures and any error codes, to the wrist-worntransceiver 72 for processing. Once the cuff-based measurement iscomplete, the cuff-based module 85 is removed from the patient's arm andthe cable 86 is disconnected from the wrist-worn transceiver 72. cNIBPis then determined using PTT, as described in detail above.

To determine an ECG, the body-worn monitor 10 features a small-scale,three-lead ECG circuit integrated directly into a bulkhead 74 thatterminates an ECG cable 82. The ECG circuit features an integratedcircuit that collects electrical signals from three chest-worn ECGelectrodes 78 a-c connected through cables 80 a-c. FIGS. 7A,B describethese systems in more detail. From these electrical signals the ECGcircuit determines up to three ECG waveforms, each corresponding to adifferent lead, which are digitized using an analog-to-digital converterwithin the integrated circuit, and sent through the cable 82 to thewrist-worn transceiver 72 according to the CAN protocol. The bulkhead 74also includes an accelerometer that measures motion associated with thepatient's chest as described above, as well as a thermocouple to measureskin temperature.

FIGS. 5A, 5B show three-dimensional views of the wrist-worn transceiver72 before and after receiving cables 82, 86, 89 from sensors worn on thepatient's upper arm and torso, as well as the cable 92 that connects tothe optical sensor. The transceiver 72 is sealed in a water-proofplastic casing 117 featuring electrical interconnects (not shown in thefigure) on its bottom surface that interface to the terminal ends 111,115 a-c of cables 82, 86, 89, 92 leading to the monitor's varioussensors. The electrical interconnects support serial communicationthrough the CAN protocol, described in detail herein, particularly withreference to FIG. 11. During operation, the transceiver's plastic casing117 snaps into a plastic housing 106, which features an opening 109 onone side to receive the terminal end 111 of the cable 92 connected tothe optical sensor. On the opposing side the plastic housing 106features three identical openings 104 a-c that receive the terminal ends115 a-c of cables 82, 86, 89 connected to the ECG and accelerometersystems (cable 82), the pneumatic cuff-based system (cable 86), andancillary systems (cable 89) described above. In addition to beingwaterproof, this design facilitates activities such as cleaning andsterilization, as the transceiver contains no openings for fluids commonin the hospital, such as water and blood, to flow inside. During acleaning process the transceiver 72 is simply detached from the plastichousing 106 and then cleaned.

The transceiver 72 attaches to the patient's wrist using a flexiblestrap 90 which threads through two D-ring openings in the plastichousing 106. The strap 90 features mated Velcro patches on each sidethat secure it to the patient's wrist during operation. The transceiver72 houses the circuits 175, 140 described in FIGS. 9B and 10 and, asshown in FIG. 5C, additionally features a touchpanel display 100 thatrenders a GUI 73. The GUI 72, for example, can be altered depending onthe viewer (typically the patient or a medical professional). Thesefeatures are described in more detail with reference to FIGS. 12A-12C.

The electrical interconnects on the transceiver's bottom side line upwith the openings 104 a-c, and each supports the CAN protocol to relay adigitized data stream to the transceiver's internal CPU. The protocolfor this process is described in detail with reference to FIG. 11. Thisallows the CPU to easily interpret signals that arrive from themonitor's body-worn sensors, and means that these connectors are notassociated with a specific cable. Any cable connecting to thetransceiver 72 can be plugged into any opening 104 a-c. As shown in FIG.5A, the first opening 104 a receives the cable 82 that transportsdigitized ECG waveforms determined from the ECG circuit and electrodes,and digitized ACC waveforms measured by accelerometers in the cablebulkhead and the bulkhead portion associated with the ECG cable 82.

The second opening 104 b receives the cable 86 that connects to thepneumatic cuff-based system used for the pressure-dependent indexingmeasurement. This connector receives a time-dependent pressure waveformdelivered by the pneumatic system to the patient's arm, along withvalues for SYS, DIA, and MAP values determined during the indexingmeasurement. The cable 86 unplugs from the opening 104 b once theindexing measurement is complete, and is plugged back in afterapproximately four hours for another indexing measurement.

The final opening 104 c can be used for an auxiliary device, e.g. aglucometer, infusion pump, body-worn insulin pump, ventilator, orend-tidal CO₂ monitoring system. As described with reference to FIG. 11,digital information generated by these systems will include a headerthat indicates their origin so that the CPU can process themaccordingly.

The transceiver includes a speaker 101 that allows a medicalprofessional to communicate with the patient using a voice over Internetprotocol (VoIP). For example, using the speaker 101 the medicalprofessional can query the patient from a central nursing station ormobile phone connected to a wireless, Internet-based network within thehospital. Or the medical professional can wear a separate transceiversimilar to the one shown in FIGS. 5A-C, and use this as a communicationdevice. In this application, the transceiver 72 worn by the patientfunctions much like a conventional cellular telephone or ‘walkietalkie’: it can be used for voice communications with the medicalprofessional and can additionally relay information describing thepatient's vital signs and motion.

FIGS. 6A-6D show, respectively, side (6A,C) and top (6B,D) views of thewrist-worn transceiver 72, and indicate how the Li:ion battery 93 can beremoved using a ‘hot swap’ configuration so that the transceiver's dataand wireless connection to the network are preserved after the batterychange. Prior to the hot swap a battery-powered dongle 97 operating afirmware program is plugged into one of the openings 104 c, as indicatedby FIG. 6A. After being plugged in, the dongle 97 sends a packetformatted according to the CAN protocol to the transceiver indicatingthat its battery is about to be replaced with one having a full charge.The transceiver receives the packet, and in response stores innon-volatile memory information that is normally not present when adevice is initially powered on. This includes the patient's vital signs,cNIBP indexing parameters, trending information, and parametersconcerning the transceiver's connection to the hospital network.Alternatively this information can be temporarily stored in a databuffer on the network, or on non-volatile memory associated with thedongle. Once this is complete, as indicated in FIG. 6B, thetransceiver's GUI renders a message that the battery 93 may be replaced.The depleted battery 93, located on the bottom side of the transceiver72, can now be replaced with a charged battery. As shown in FIG. 6D,after this operation is complete the GUI renders a virtual button that,once pressed, will reset the transceiver 72 to return it to itsconfiguration before the battery swap. The transceiver then downloadsthe above-described information stored in either internal non-volatilememory, on the network, or in the dongle 97, and then the dongle 97 isremoved from the opening 104 c. The transceiver 72 then returns tomonitoring the patient.

Configurable ECG System

FIGS. 7A, B show a configurable ECG system 74 integrated within thebody-worn monitor and can accommodate three, five, or twelve lead ECGconfigurations. The figure shows a system that includes three leads. Asdescribed above, the entire ECG system 74, including systems fordifferentially amplifying, filtering, and digitizing ECG signals, ismounted on a circuit board disposed at a distal end of the ECG cable 82.Preferably this system is based on a single ASIC which is a small-scale,low-power, single-chip solution and can be easily incorporated in theform factor shown in FIG. 7A. Alternatively the ECG system can becomposed of a series of discrete components making up the system'srequisite filters and amplifiers. Using the CAN protocol, the ECG system74 sends digital ECG information (e.g. ECG waveforms corresponding toeach lead, heart rate and respiratory rate values, error codes) in theform of packets to the wrist-worn transceiver 72. All ECG information isprocessed and digitized before being transmitted, which means alow-profile, five-wire cable 82 is adequate for three, five, andtwelve-lead ECG systems. These different systems are typically embeddedin unique cables, which can be easily swapped in and out and applied tothe patient, and are labeled appropriately. A medical professional canincorporate them into the body-worn monitor simply by plugging thedesired cable into any CAN connector on the wrist-worn transceiver 72,and then attaching the appropriate ECG leads to the patient. The ECGsystem sends packets indicating how many leads it includes to thetransceiver, which then processes this information accordingly.

FIG. 7B shows a high-level schematic drawing of a three-lead ECG system74 that connects to the wrist-worn transceiver 72 in FIG. 7A. The ECGsystem 75 includes three electrode lead wires 80 a-c that connect,respectively, to separate electrodes 78 a-c. These are typicallydisposable adhesive electrodes worn on the patient's chest in anEinthoven's triangle configuration, as shown in FIG. 7A. During ameasurement, each electrode 78 a-c measures a unique electrical signalfrom the patient's chest which then propagates through the lead wires 80a-c to the single-chip ECG processor 120, described above. The ECGprocessor 120 differentially amplifies the ECG signals from eachelectrode 78 a-c, and then filters and further amplifies the resultingwaveform according to parameters which can be configured with amicrocontroller 122 within the ECG system 74. The microcontroller 122interfaces to a crystal 126 (typically operating at 100 kHz) and a clockdivider 127 that processes incoming timing packets, as is described inmore detail below with reference to FIG. 11. The ECG processor 120includes an internal analog-to-digital converter that digitizes uniquewaveforms corresponding to each lead. It then processes the digitizedwaveforms to determine heart rate and parameters describing thepatient's cardiac condition, e.g. VTAC, VFIB, and PVCs. The ECGprocessor 120 can also drive one of the electrodes (e.g. electrode 78 a)with a modulated current, as described above, and detect this currentalong with breathing-induced modulations with a second electrode (e.g.electrode 78 b) to determine respiratory rate according to impedancepneumography.

Once this information is determined, a CAN controller 124 within the ECGcircuit 74 processes the resulting data and transmits it as a series ofCAN packets to the wrist-worn transceiver 72, described in detail below.Values for heart rate, respiratory rate, and one of the time-dependentECG waveforms (typically the Lead II waveform), along with alarms/alertsrelated to cardiac parameters such as VTAC, VFIB, and PVCs, are thendisplayed on the transceiver's GUI. One of the ECG waveforms isprocessed to determine blood pressure according to the CompositeTechnique. The transceiver 72 relays all the information it receivesfrom the ECG system 74 to a server connected to the in-hospital network.

Removable Pneumatic System

FIGS. 8A-C show an exemplary cuff-based system 85 used within thebody-worn sensor to make pressure-dependent measurements according tothe Composite Technique. Within the cuff-based system 85 is a pneumaticsystem 76 featuring a single motherboard 135 that includes components139 similar to those shown in FIG. 7B (microcontroller, crystaloscillator, clock divider, CAN transceiver) to processpressure-dependent waveforms and communicate with the wrist-worntransceiver 72. To power these components, the pneumatic system 76additionally includes a separate Li:ion battery (not shown in thefigure) that connects through connector 137. This battery is similar tothat used in the transceiver 72. A CAN connector 136 receives the cable86 so that the pneumatic system 76 can transmit information to thewrist-worn transceiver 72.

To measure the pressure waveform during a pressure-dependentmeasurement, the pneumatic system 76 features a small mechanical pump133 that inflates a bladder within the cuff 84, which is worn around thepatient's bicep and features a pneumatic connector (not shown in thefigure) that the pneumatic system 76 plugs into. The system 76 featurestwo solenoid valves 132, 163, each controlled by a separatemicrocontroller mounted on the motherboard, and configured to connectthe pump 133 to an outside air reservoir to inflate the cuff. Bothsolenoid valves 132, 163 and the pump 133 connect through a manifold 131to an opening 141 that attaches through a connector (not shown in thefigure) to the bladder within the armband, and additionally to a pair ofpressure sensors 134 a,b that sense the pressure in the bladder. Theopening 141 is covered by a screw-in plug 138 to prevent build up ofdebris in the manifold 131 when the pneumatic system 76 is not attachedto the cuff 84. A primary solenoid valve 132 is normally closed when notactivated (i.e., when power is not applied). The secondary solenoidvalve 163 has the opposite configuration, and is normally open when notactivated. When both valves 132, 163 are activated (i.e., when power isapplied), the primary valve 132 opens and the secondary valve 163closes, thus providing a path for the pump 133 to funnel air through themanifold 131 and to the cuff 84. During a measurement, heartbeat-inducedpulsations couple into the bladder as it inflates, and are subsequentlymapped onto a pressure waveform. The pressure sensors 134 a,b generatedigital pressure waveforms which are filtered and processed by themicrocontroller to measure blood pressure during inflation, as describedabove. The first pressure sensor 134 a generates a pressure waveformthat is used for the cuff-based indexing measurement, while the secondsensor 134 b is used as a back-up in case the first sensor 134 a fails.Once complete, blood pressure values are used to index the PTT-basedpressure-free measurements as described above. When the measurement iscomplete, the valves 132, 163 are deactivated, and the pump 133 is nolonger powered, causing the cuff 84 to rapidly deflate. The cuff 84 andcuff-based system 85 is then removed, and follow-on cNIBP measurementsare calculated from PTT as described above.

Optical Sensor for cNIBP and SpO2

FIGS. 9A, B show an exemplary optical sensor 94 that measures PPGsignals from both red and infrared LEDs which the wrist-worn transceiver72 processes to determine cNIBP and SpO2. The sensor 94 includes a dualLED 296 operating at 660 and 905 nm, depending on the direction of bias,a photodetector 155 for detecting radiation from the LED 296 after itpasses through a portion of the patient's thumb, and a laser-trimmedresistor 295 indicating the specific wavelength of the red portion ofthe dual LED 296, as described below. Powering these components is acircuit 175 within the wrist-worn transceiver that generatestime-dependent current pulses to drive the LEDs. The circuit 175features an operational amplifier 180 that receives a control voltage(V_(control)) on its gating pin. The amplifier 180 is connected to atransistor 182 and resistor 181 that, along with a supply voltage of3.3V (typically from a Li:ion battery), generate the current pulses usedto drive the dual LED 296. To select the biasing direction of the LED,and thus choose the wavelength that is emitted, the circuit 175 featuresred control lines 185, 190 and infrared control lines 187, 189 thatconnect directly to I/O lines in the CPU within the wrist-worntransceiver. During a measurement, current pulses flow from the 3.3Vsupply voltage, across one direction of the LED 296, and ultimatelythrough the transistor 182 and resistor 181 to ground 183. The LED 296is biased in a forward direction when control lines 185, 190 are toggledclosed, thereby supplying a drive current pulse ofi_(LED)=V_(control)/R₁ to the LED 296 to generate red radiation. Voltageflowing across the LED 296 is also decreased because it is a diode. Inthis case the control lines 187, 189 for infrared radiation are leftopen. This configuration persists for 100 μs, after which the redcontrol lines 185, 190 are switched closed, and the infrared controllines 187, 189 are switched open. This biases the LED 296 in a backwardsdirection to generate infrared radiation according to theabove-described drive current. The alternating process is repeated at500 Hz.

During a measurement, the CPU in the wrist-worn transceiver determinesthe value of the resistor 295 by monitoring a voltage drop across it;this value, in turn, is compared to a value stored in memory to selectthe appropriate coefficients relating a parameter called a ‘ratio ofratios’ (RoR) to SpO2. This calculation is described in detail in theabove-referenced patent application describing SpO2, the contents ofwhich have been incorporated herein by reference. The probe 94 generatesalternating red and infrared radiation at 500 Hz that passes through thebase of the patient's thumb 151, where it is partially absorbed byunderlying vasculature according to the patient's heart rate and SpO2values. Radiation that transmits through the thumb 151 illuminates aphotodiode 155 that, in response, generates a photocurrent varying inmagnitude with the degree of optical absorption in the patient's thumb.An amplifier circuit 140 beginning with a transimpedance amplifier 156receives the photocurrent and converts it to a corresponding voltagewhich is then amplified and filtered to generate the PPGs waveforms withboth red and infrared wavelengths used to determine SpO2 and cNIBP.

The amplifier circuit 140 features separate channels for amplifying andfiltering signals corresponding to red radiation, infrared radiation,and ambient light detected by the photodiode 155 when the LED is notbiased to generate radiation. This occurs, for example, during the timeperiods when neither the red or infrared LED is driven. Once detected,the degree of ambient light can be subtracted from both the red andinfrared signals to improve their resultant signal-to-noise ratio. Theamplifier channel corresponding to red radiation is activated by asample-and-hold integrated circuit 157 that is controlled by the samecontrol lines 185, 190 that drive the red LED, as shown in FIG. 9B. Whenthe red LED is driven, the sample-and-hold circuit 157 is switched on,while similar components 164, 172 corresponding to the infrared signalsand ambient light are switched off. The sample-and-hold circuit 157samples and maintains an analog voltage from the transimpedanceamplifier 156, which then passes through a low-pass filter 158characterized by a 20 Hz cutoff. This filter removes any high-frequencynoise (e.g. 60 Hz electrical noise) that is not related to the PPGwaveform, and yields a preliminary waveform that is digitized with ananalog-to-digital converter 176, and processed as described above togenerate a DC portion of the PPG. The preliminary waveform then passesthrough a high-pass filter 160 with a cutoff of 0.1 Hz to remove the DCportion and leave only the AC portion, which typically represents about0.5-1% of the total signal magnitude. The AC portion is furtheramplified with a standard instrumentation amplifier 162 featuring aprogrammable gain that is controlled with a 1.65 reference voltage and adigital potentiometer (not shown in the figure; this component may beincluded directly in the instrumentation amplifier) featuring a variableresistance controlled by the CPU within the wrist-worn transceiver. TheCPU selects the resistance (according to a predetermined command) andcorresponding gain to maximize the dynamic range of theanalog-to-digital converter 176. This process results in an amplifiedversion of the AC portion of the red PPG waveform, which is thendigitized with the analog-to-digital converter 176 and then processed asdescribed above.

The above-described filtering and amplification processes are repeatedwhen the infrared LED and a sample-and-hold integrated circuit 164corresponding to the infrared channel are activated with infraredcontrol lines 187, 189. The low-pass 166 and high-pass 168 filterscorresponding to this channel are identical to those used for the redchannel. The instrumentation amplifier 170 is also identical, but iscontrolled by a separate digital potentiometer to have a unique,uncoupled gain. This is because the infrared PPG waveform typically hasa relatively large amplitude, and thus requires less amplification, thanthe red PPG waveform. The channel corresponding to ambient light onlyrequires processing of DC signals, and thus includes a sample-and-holdintegrated circuit 172 that passes an analog voltage to a low-passfilter 174 featuring a 20 Hz cutoff. The filtered value corresponding toambient light is then digitized with the analog-to-digital converter andthen processed as described above.

A five-wire cable, similar to that used for the ECG and pneumaticsystems, connects the thumb-worn optical sensor to the wrist-worntransceiver. Black circles in FIG. 9B indicate where wires in the cableconnect to circuit elements in the thumb-worn sensor (only four dots areshown; the fifth connection is a conducting shield for the remaining 4wires). Note that the value for the laser-trimmed resistor is determinedby a voltage drop when both control lines for the red 185, 190 andinfrared 187, 189 are open. In this configuration there is no biasacross the LED, so radiation is not emitted, but there is a smallvoltage drop across the infrared control lines 187, 189 due to theresistor 295. The resistor value is chosen to be sufficiently small sothat only a small amount of current is drawn during an actualmeasurement.

Communicating with Multiple Systems Using the CAN Protocol

As described above, the ECG, ACC, and pneumatic systems within thebody-worn system can send digitized information to the wrist-worntransceiver through the CAN protocol. FIG. 11 shows a schematic drawingindicating how CAN packets 201 a-d, 212 a-e transmitted between thesesystems facilitate communication. Specifically, each of the ACC 14, ECG74, pneumatic 76, and auxiliary 45 systems include a separateanalog-to-digital converter, microcontroller, frequency-generatingcrystal oscillator (typically operating at 100 kHz), and real-time clockdivider that collectively generate and transmit digital data packets 201a-d according to the CAN protocol to the wrist-worn transceiver 72. Eachcrystal uses the internal real-time clock on the internal microprocessorwithin the respective system. This allows the microcontroller withineach system to be placed in a low-power state in which its real-timeoperating system (RTOS) dispatch system indicates that it is not readyto run a task. The real-time clock divider is programmed to create aninterrupt which wakes up the microcontroller every 2 milliseconds.

The wrist-worn transceiver 72 features a ‘master clock’ that generatesreal-time clock ‘ticks’ at the sampling rate (typically 500 Hz, or 2 msbetween samples). Each tick represents an incremented sequence number.Every second, the wrist-worn transceiver 72 transmits a packet 212 eover the CAN bus that digitally encodes the sequence number. One of thecriteria for accurate timing is that the time delay between theinterrupt and the transmission of the synchronizing packet 212 e, alongwith the time period associated with the CAN interrupt service routine,is predictable and stable. During initialization, the remote CAN busesdo not sleep; they stay active to listen for the synchronization packet212 e. The interrupt service routine for the synchronization packet 212e then establishes the interval for the next 2 millisecond interruptfrom its on-board, real-time crystal to be synchronized with the timingon the wrist-worn transceiver 72. Offsets for the packet transmissionand interrupt service delays are factored into the setting for thereal-time oscillator to interrupt synchronously with the microprocessoron the wrist-worn transceiver 72. The magnitude of the correction factorto the real-time counter is limited to 25% of the 2 millisecond intervalto ensure stability of this system, which represents a digitalphase-locked loop.

When receipt of the synchronization packet 212 e results in a timingcorrection offset of either a 0, +1, or −1 count on the remote system'soscillator divider, software running on the internal microcontrollerdeclares that the system is phase-locked and synchronized. At thispoint, it begins its power-down operation and enables measurement ofdata as described above.

Each remote system is driven with a 100 kHz clock, and a single count ofthe divider corresponds to 20 microseconds. This is because the clockdivider divides the real-time clock frequency by a factor of 2. This isinherent in the microcontroller to ensure that the clock has a 50% dutycycle, and means the clock can drift +/−20 microseconds before theactual divider chain count will disagree by one count, at which time thesoftware corrects the count to maintain a phase-locked state. There isthus a maximum of 40 microseconds of timing error between datatransmitted from the remote systems over the CAN bus. Blood pressure isthe one vital sign measured with the body-worn monitor that iscalculated from time-dependent waveforms measured from different systems(e.g. PPG and ECG waveforms). For this measurement, the maximum40-microsecond timing error corresponds to an error of +/−0.04 mmHg,which is well within the error (typically +/−5 mmHg) of the measurement.

In order to minimize power consumption, the wrist-worn transceiver 72and remote systems 14, 74, 76, 45 power down their CAN bus transceiversbetween data transfers. During a data transfer, each system generates asequence number based on the synchronization packet 212 e, and includesthis in its packet. The sequence number represents the interval betweendata transfers in intervals of 2 milliseconds. It is a factor of 500(e.g. 2, 4, 5, 10) that is the number of 2 millisecond intervals betweentransfers on the CAN bus. Each remote system enables its CAN bus duringthe appropriate intervals and sends its data. When it has finishedsending its data, it transmits a ‘transmit complete’ packet indicatingthat the transmission is complete. When a device has received the‘transmit complete’ packet it can disable its CAN transceiver to furtherreduce power consumption.

Software in each of the ACC 14, ECG 74, pneumatic 76, and auxiliary 45systems receive the sequence packet 212 e and the corresponding sequencenumber, and set their clocks accordingly. There is typically someinherent error in this process due to small frequency differences in thecrystals (from the ideal frequency of 100 kHz) associated with eachsystem. Typically this error is on the order of microseconds, and hasonly a small impact on time-dependent measurements, such as PTT, whichare typically several hundred milliseconds.

Once timing on the CAN bus is established using the above-describedprocedure, each of the ACC 14, ECG 74, and pneumatic 76 systems generatetime-dependent waveforms that are transmitted in packets 201 a-d, eachrepresenting an individual sample. Each packet 201 a-d features a headerportion which includes the sequence number 212 a-d and an initial value210 a-d indicating the type of packet that is transmitted. For example,accelerometers used in the body-worn system are typically three-axisdigital accelerometers, and generate waveforms along the x, y, andz-axes. In this case, the initial value 210 a encodes numerical valuesthat indicate: 1) that the packet contains ACC data; and 2) the axis (x,y, or z) over which these data are generated. Similarly, the ECG system204 can generate a time-dependent ECG waveform corresponding to Lead I,II, or III, each of which represents a different vector measured alongthe patient's torso. Additionally, the ECG system 204 can generateprocessed numerical data, such as heart rate (measured from timeincrements separating neighboring QRS complexes), respiratory rate (froman internal impedance pneumography component), as well as alarmscalculated from the ECG waveform that indicate problematiccardiovascular states such as VTAC, VFIB, and PVCs. Additionally, theECG system can generate error codes indicating, for example, that one ofthe ECG leads has fallen off. The ECG system typically generates analarm/alert, as described above, corresponding to both the error codesand potentially problematic cardiovascular states. In this case, theinitial value 210 b encodes numerical values that indicate: 1) that thepacket contains ECG data; 2) the vector (Lead I, II, or III)corresponding to the ECG data; and 3) an indication if a cardiovascularstate such as VTAC, VFIB, or PVCs was detected by the ECG system.

The pneumatic system 76 is similar to the ECG system in that itgenerates both time-dependent waveforms (i.e. a pressure waveform,measured during oscillometry, characterizing the pressure applied to thearm and subsequent pulsations measured during an oscillometricmeasurement) and calculated vital signs (SYS, DIA, and MAP measuredduring oscillometry). In some cases errors are encountered during theoscillometric blood pressure measurement. These include, for example,situations where blood pressure is not accurately determined, animproper OSC waveform, over-inflation of the cuff, or a measurement thatis terminated before completion. In these cases the pneumatic system 76generates a corresponding error code. For the pneumatic system 76 theinitial value 210 c encodes numerical values that indicate: 1) that thepacket contains blood pressure data; 2) an indication that the packetincludes an error code.

In addition to the initial values 210 a-d, each packet 201 a-d includesa data field 214 a-d that encodes the actual data payload. Examples ofdata included in the data fields 214 a-d are: 1) sampled values of ACC,ECG, and pressure waveforms; 2) calculated heart rate and blood pressurevalues; and 3) specific error codes corresponding to the ACC 14, ECG 74,pneumatic 76, and auxiliary 25 systems.

Upon completion of the measurement, the wrist-worn transceiver 72receives all the CAN packets 201 a-d, and synchronizes them in timeaccording to the sequence number 212 a-d and identifier 210 a-d in theinitial portions 216 of each packet. Every second, the CPU updates thetime-dependent waveforms and calculates the patient's vital signs andmotion-related properties, as described above. Typically these valuesare calculated as a ‘rolling average’ with an averaging window rangingfrom 10-20 seconds. The rolling average is typically updated everysecond, resulting in a new value that is displayed on the wrist-worntransceiver 72. Each packet received by the transceiver 72 is alsowirelessly retransmitted as a new packet 201 b′ to a remote computer 43connected to an in-hospital network. The new packet 201 b′ includes thesame header information 210 b′, 212 b′ and data field information 214 b′as the CAN packets transmitted between systems within the body-wornmonitor. Also transmitted are additional packets encoding the cNIBP,SpO2, and processed motion states (e.g. posture, activity level, degreeof motion), which unlike heart rate and SYS, DIA, and MAP are calculatedby the CPU in the wrist-worn transceiver. Upon receipt of the packet 201b′, the remote computer 43 displays vital signs, waveforms, motioninformation, and alarms/alerts, typically with a large monitor that iseasily viewed by a medical professional. Additionally the remotecomputer 43 can send information through the hospital network (e.g. inthe case of an alarm/alert), and store information in an internaldatabase.

Displaying Information Using Graphical User Interfaces

Referring to FIGS. 12A-C, the transceiver 72 features a touch paneldisplay 100 that renders a multi-window GUI 73 which can be tailored toboth medical professionals and the patient. To select the appropriateGUI, the transceiver 72 includes a small-scale infrared barcode scanner102 that emits radiation 120 to scan a barcode 122 worn on a badge 121of a medical professional. Information encoded on the barcode 122 iscompared to a database stored within the transceiver 72 to indicate, forexample, that a nurse or doctor is viewing the user interface. Thisdatabase can be updated through the hospital's network. In response, theGUI 73 displays vital sign data, waveforms, alarms/alerts and othermedical diagnostic information appropriate for medical professionals, asshown by the screen 297 in FIG. 12B. Using this GUI 73, the medicalprofessional can view the vital sign information, set alarm parameters,and enter information about the patient (e.g. their posture, demographicinformation, medication, or medical condition). The nurse can press a‘Patient View’ button on the GUI 73 indicating that these operations arecomplete. The patient view is shown by the screen 125 in FIG. 12C, andpurposefully lacks any content related to vital signs. Instead isdesigned to be relatively generic, featuring the time, date, and iconsindicating the patient's activity level, whether or not an alarm hasbeen generated, battery life, and wireless signal strength. The GUI alsofeatures a graphical ‘call nurse’ button that, once depressed,wirelessly sends a signal to the central nursing station indicating thatthe patient needs assistance from a nurse. The patient view screen 125includes a button labeled ‘UNLOCK’ that, once activated, allows a nurseor doctor to activate the medical professional view 297 shown in FIG.11B. Tapping the UNLOCK button powers the barcode scanner in thebody-worn monitor; this scans a barcode printed on a badge of the nurseof doctor, as described above, and prompts the monitor to render themedical professional view screen 297, shown in FIG. 12B.

The medical professional view screen 297 is designed to have a ‘look andfeel’ similar to each area 108 of the GUI on the nursing stationcomputer, as shown in FIG. 15A. This makes it relatively easy for thenurse to interpret information rendered on both the body-worn monitorand remote monitor. The screen 297 features fields for a patientidentifier, numerical values for vital signs, a time-dependent ECGwaveform with a span of approximately 5 seconds, and icons indicatingbattery life, wireless signal strength, and whether or not an alarm hasbeen generated. A fixed bar proximal to the ECG waveform indicates asignal strength of 1 mV, as required by the AAMI:ANSI EC13 specificationfor cardiac monitors.

The GUI operating on both the body-worn module and the remote monitorcan render graphical icons that clearly identify patient activitystates, determined as described above from the ACC waveforms. FIG. 13shows examples of such icons 105 a-h, and Table 1, below, describes howthey correspond to specific patient activity states. As shown in FIGS.12A-C and 15A, these icons are used in GUIs for both the body-wornmonitor and remote monitor.

TABLE 1 description of icons shown in FIG. 13 and used in GUIs for bothbody-worn monitor and remote monitor Icon Activity State 105a Standing105b Falling 105c Resting; lying on side 105d Convulsing 105e Walking105f Sitting 105g Resting; lying on stomach 105h Resting; lying on back

FIG. 14 indicates how the wrist-worn transceiver 72 can communicatewirelessly with either a networked computer 198 (e.g. a tablet computerlocated at a central nursing station) or a hand-held computer 199 (e.g.a cell phone or PDA, typically carried by the medical professional). Thespecific form of the communication can be determined either manually orautomatically. For example, in a normal mode of operation the patientwears the transceiver in their hospital room, and it wirelesslytransmits information as described above though a wireless network tothe computer 198. Typically this is a network based on 802.11, which iscommonplace in the hospital. In a normal mode of operation the computeris associated with a group of patients in an area of the hospital (e.g.a bay of hospital beds, or an ED), and the computer 198 renders a GUIthat shows summary information relating to vital signs, motion-relatedparameters, and alarms/alerts for each patient in the area. A medicalprofessional can ‘drill down’ on a particular patient by clicking on theportion of the GUI that displays their information.

In another mode of operation, the medical professional can carry thecomputer 198 into the patient's hospital room for a consultation. Inthis case, software running on the computer 198 can detect a relativelystrong wireless signal strength (RSSI value) associated with theproximal patient, and render their information with the GUI.Alternatively, as described above, the medical professional can manuallyselect this information.

Most portable cellular phones and PDAs have built-in wirelesscapabilities based on 802.11 and 802.15.4, and thus the wrist-worntransceiver 72 can wirelessly communicate with these devices with apeer-to-peer communication protocol. Typically, in this case, theportable device 199 includes a software application that has beendownloaded into its memory, typically from a web-based server. Tomonitor a particular patient, the medical professional uses the softwareapplication to select a particular patient. This process ‘pairs’ theportable device with the patient's wrist-worn transceiver 72. Oncepaired, the transceiver sends information for the particular patient tothe portable device 199, which then displays it for the medicalprofessional. In other embodiments, the portable device can communicatewith the hospital network so that the medical professional can viewinformation for a particular patient even if they are in a differentarea of the hospital. In still other embodiments, the hospital networkis accessible through a cellular network associated with the portabledevice, and the medial professional can select and view information fora particular patient from any remote location, provided it has goodcoverage in the cellular network.

FIGS. 15A and 15B show patient (106 in FIG. 15A) and map (107 in FIG.15B) views from a GUI typically rendered on a remote monitor 198, suchas that described above. For example, the different views 106, 107 aregenerated when a medical professional clicks icons on a GUI rendered bythe remote monitor 198 that correspond, respectively, to vital signs 197and location 196. To generate the GUI the remote monitor 198simultaneously communicates with multiple body-worn monitors, eachdeployed on a patient in an area of the hospital. The patient view 106is designed to give a medical professional, such as a nurse or doctor, aquick, easy-to-understand status of all the patients of all the patientsin the specific hospital area. In a single glance the medicalprofessional can determine their patients' vital signs, measuredcontinuously by the body-worn monitor, along with their activity stateand alarm status. The view 106 features a separate area 108corresponding to each patient. Each area 108 includes text fieldsdescribing the name of the patient and supervising clinician; numbersassociated with the patient's bed, room, and body-worn monitor; and thetype of alarm generated from the patient. As described above, this area108 has a similar ‘look and feel’ to the interface rendered on thewrist-worn transceiver. Graphical icons, similar to those shown in FIG.14, indicate the patient's activity level. Additional icons show thebody-worn monitor's battery power, wireless signal strength, and whetheror not an alarm has been generated. Each area 108 also clearly indicatesnumerical values for each vital sign measured continuously by thebody-worn monitor. The monitor displaying the patient view 106 typicallyincludes a touchpanel. Tapping on the patient-specific area 108generates a new view (not shown in the figure) that expands all theinformation in the area 108, and additionally shows time-dependent ECGand PPG waveforms corresponding to the patient.

FIG. 15B shows a map view 107 that indicates the location and activitystate of each patient in the hospital area. Each patient's location istypically determined by processing the wireless signal from theirbody-worn monitor (e.g., by triangulating on signals received byneighboring 802.11 base stations, or simply using proximity to the basestation) or by using more advanced methods (e.g. time-of-flight analysisof the wireless signal, or conventional or network-assisted GPS), bothof which are done using techniques known in the art. The patient'slocation is mapped to a grid representing the distribution of beds inthe hospital area to generate the map view 107. The map view 107typically refreshes every 10-20 seconds, showing an updated location andactivity state for each patient.

Continuous Patient Monitoring in the Hospital

FIG. 16 shows one possible sequence 278 of how the body-worn monitordescribed above can characterize a hospitalized patient using theComposite Technique, which includes an initial pressure-dependent (step282 a), pressure-free (steps 281 a, 281 b, 281 c), and intermediatepressure-dependent (steps 282 b, 282 c) measurements for a patientundergoing an extended hospital stay. During the stay, a medicalprofessional applies the body-worn monitor to the patient (step 280).This takes about 1 minute. The medical professional may also collectbiometric information from the patient, such as their age, weight,height, gender, ethnicity, and whether they are on blood pressuremedications, and enter these into the monitor using a GUI andtouchpanel, as described above. This information is then communicatedwirelessly through the hospital network. Going forward, the CPU withinthe wrist-worn transceiver first initiates a pressure-free measurement(step 281 a) for about 1 minute, wherein the body-worn monitor collectsPPG and ECG waveforms from the patient to determine their heart rate andPTT values. In the absence of an absolute blood pressure measurementfrom the Composite Technique's pressure-dependent measurement, themicroprocessor may use PTT and the patient's biometric information toestimate blood pressure, as is described in the following co-pendingpatent application, the contents of which are fully incorporated hereinby reference: 1) DEVICE AND METHOD FOR DETERMINING BLOOD PRESSURE USING‘HYBRID’ PULSE TRANSIT TIME MEASUREMENT (U.S. Ser. No. 60/943,464; filedJun. 12, 2007); and 2) VITAL SIGN MONITOR FOR CUFFLESSLY MEASURING BLOODPRESSURE CORRECTED FOR VASCULAR INDEX (U.S. Ser. No. 12/138,199; filedJun. 12, 2008). This process typically determines systolic and diastolicblood pressure with an accuracy of about ±10-15 mmHg.

The initial, approximate value for the patient's blood pressure andheart rate determined during the first pressure-free measurement (step281 a) can then be used to set certain parameters during the followingfirst pressure-dependent measurement (step 282 a). Knowledge of theseparameters may ultimately increase the accuracy of the initialpressure-dependent measurement (step 282 a). Such parameters, forexample, may include inflation time and rate, fitting parameters fordetermining the time-dependent increase in PTT and the time-dependentdecrease in PPG waveform amplitude during the pressure-dependentmeasurement. Of particular importance is an accurate value of thepatient's heart rate determined during the first pressure-freemeasurement (step 281 a). Since both PTT and amplitude can only bemeasured from a pulse induced by a heartbeat, the algorithm can processheart rate and use it in the fitting process to accurately determine thepressure at which the PPG waveform amplitude crosses zero.

Using parameters such as heart rate and initial estimated bloodpressure, the first pressure-dependent measurement (step 282 a)determines a relationship between PTT and blood pressure as describedabove. This takes about 60 seconds. This measurement may occurautomatically (e.g., after about 1 minute), or may be driven by themedical professional (e.g., through a button press). The microprocessorthen uses this relationship and a measured value of PTT to determineblood pressure during the following pressure-free measurement (step 281b). This measurement step typically proceeds for a well-defined periodof time (typically 4-8 hours), during which it continuously determinesblood pressure. Typically, the body sensor averages PTT values over a10-20 second period, and displays a new blood pressure measurement everysecond using a rolling average.

The microprocessor may also perform a pre-programmed or automatedintermediate pressure-dependent measurement (step 282 b) to correct anydrift in the blood pressure measurement. This measurement is similar tothe initial pressure-dependent measurement 282 a. At some later time, ifthe patient experiences a sudden change in other vital signs (e.g.,respiratory rate, heart rate, body temperature), the CPU in thewrist-worn transceiver may analyze this condition and initiate anotherpressure-dependent blood pressure measurement (step 282 c) to mostaccurately determine the patient's blood pressure.

In addition to those methods described above, a number of additionalmethods can be used to calculate blood pressure from the PPG and ECGwaveforms. These are described in the following co-pending patentapplications, the contents of which are incorporated herein byreference: 1) CUFFLESS BLOOD-PRESSURE MONITOR AND ACCOMPANYING WIRELESS,INTERNET-BASED SYSTEM (U.S. Ser. No. 10/709,015; filed Apr. 7, 2004); 2)CUFFLESS SYSTEM FOR MEASURING BLOOD PRESSURE (U.S. Ser. No. 10/709,014;filed Apr. 7, 2004); 3) CUFFLESS BLOOD PRESSURE MONITOR AND ACCOMPANYINGWEB SERVICES INTERFACE (U.S. Ser. No. 10/810,237; filed Mar. 26, 2004);4) VITAL SIGN MONITOR FOR ATHLETIC APPLICATIONS (U.S. Ser. No.; filedSep. 13, 2004); 5) CUFFLESS BLOOD PRESSURE MONITOR AND ACCOMPANYINGWIRELESS MOBILE DEVICE (U.S. Ser. No. 10/967,511; filed Oct. 18, 2004);6) BLOOD PRESSURE MONITORING DEVICE FEATURING A CALIBRATION-BASEDANALYSIS (U.S. Ser. No. 10/967,610; filed Oct. 18, 2004); 7) PERSONALCOMPUTER-BASED VITAL SIGN MONITOR (U.S. Ser. No. 10/906,342; filed Feb.15, 2005); 8) PATCH SENSOR FOR MEASURING BLOOD PRESSURE WITHOUT A CUFF(U.S. Ser. No. 10/906,315; filed Feb. 14, 2005); 9) PATCH SENSOR FORMEASURING VITAL SIGNS (U.S. Ser. No. 11/160,957; filed Jul. 18, 2005);10) WIRELESS, INTERNET-BASED SYSTEM FOR MEASURING VITAL SIGNS FROM APLURALITY OF PATIENTS IN A HOSPITAL OR MEDICAL CLINIC (U.S. Ser. No.11/162,719; filed Sep. 9, 2005); 11) HAND-HELD MONITOR FOR MEASURINGVITAL SIGNS (U.S. Ser. No. 11/162,742; filed Sep. 21, 2005); 12) CHESTSTRAP FOR MEASURING VITAL SIGNS (U.S. Ser. No. 11/306,243; filed Dec.20, 2005); 13) SYSTEM FOR MEASURING VITAL SIGNS USING AN OPTICAL MODULEFEATURING A GREEN LIGHT SOURCE (U.S. Ser. No. 11/307,375; filed Feb. 3,2006); 14) BILATERAL DEVICE, SYSTEM AND METHOD FOR MONITORING VITALSIGNS (U.S. Ser. No. 11/420,281; filed May 25, 2006); 15) SYSTEM FORMEASURING VITAL SIGNS USING BILATERAL PULSE TRANSIT TIME (U.S. Ser. No.11/420,652; filed May 26, 2006); 16) BLOOD PRESSURE MONITOR (U.S. Ser.No. 11/530,076; filed Sep. 8, 2006); 17) TWO-PART PATCH SENSOR FORMONITORING VITAL SIGNS (U.S. Ser. No. 11/558,538; filed Nov. 10, 2006);and, 18) MONITOR FOR MEASURING VITAL SIGNS AND RENDERING VIDEO IMAGES(U.S. Ser. No. 11/682,177; filed Mar. 5, 2007).

Other embodiments are also within the scope of the invention. Forexample, other measurement techniques, such as conventional oscillometrymeasured during deflation, can be used to determine SYS for theabove-described algorithms. Additionally, processing units and probesfor measuring SpO2 similar to those described above can be modified andworn on other portions of the patient's body. For example, probes withfinger-ring configurations can be worn on fingers other than the thumb.Or they can be modified to attach to other conventional sites formeasuring SpO2, such as the ear, forehead, and bridge of the nose. Inthese embodiments the processing unit can be worn in places other thanthe wrist, such as around the neck (and supported, e.g., by a lanyard)or on the patient's waist (supported, e.g., by a clip that attaches tothe patient's best). In still other embodiments the probe and processingunit are integrated into a single unit.

Still other embodiments are within the scope of the following claims.

What is claimed is:
 1. A system for monitoring vital signs from a group of patients, comprising: (a) a monitoring device configured to be worn on the body of each patient in the group, each monitoring device comprising: a wireless system; a first sensor configured to generate a first time-dependent waveform indicative of one or more contractile properties of the patient's heart; a second sensor configured to generate a second time-dependent waveform indicative of one or more contractile properties of the patient's heart; and a processing component configured to: (i) receive a first signal representing the first time-dependent waveform; (ii) receive a second signal representing the second time-dependent waveform; (iii) calculate a blood pressure value from a pulse transit time measured between the first and second signals or versions thereof; and (iv) transmit the blood pressure value with the wireless system; and (b) a remote display device in communication with each monitoring device through the wireless system comprised by the monitoring device, the remote display device configured to simultaneously display a blood pressure value for each patient in the group when a signal strength corresponding to the wireless system comprised by each monitoring device is below a pre-determined threshold value, and further configured to automatically reconfigure the display device to display a blood pressure value for only a particular patient when the signal strength from the wireless system worn by the particular patient exceeds the pre-determined threshold.
 2. The system of claim 1, wherein the signal strength represents a magnitude of a wireless signal transmitted from a monitoring device.
 3. The system of claim 2, wherein the pre-determined threshold value is between −100 and −80 dB.
 4. The system of claim 1, wherein the wireless system comprised by each monitoring device operates on a protocol selected from 802.11, 802.15.4, and cellular wireless protocols.
 5. The system of claim 4, wherein the remote display device is further configured to simultaneously communicate with each monitoring device through a wireless network when the signal strength corresponding to the wireless system comprised by each monitoring device is below the pre-determined threshold value.
 6. The system of claim 5, wherein the wireless network is a peer-to-peer wireless connection.
 7. The system of claim 1, wherein the remote display comprises a first user interface configured to simultaneously display a blood pressure value for each patient in the group.
 8. The system of claim 7, wherein the first user interface comprises separate fields for displaying the first time-dependent waveform and the blood pressure value for each patient in the group.
 9. The system of claim 8, wherein the first time-dependent waveform is an ECG waveform.
 10. The system of claim 8, wherein each monitoring device further includes a motion-detecting sensor, and the processing component of each monitoring device is further configured to analyze a signal from the motion-detecting sensor to determine at least one of a posture, activity level, and degree of motion corresponding to the patient wearing the monitoring device.
 11. The system of claim 10, wherein the first user interface comprises a separate field for displaying at least one of the posture, activity level, and degree of motion corresponding to each patient wearing the monitoring device.
 12. The system of claim 7, wherein the processing component of each monitoring device is further configured to analyze wireless signals from at least one wireless base station to estimate a location of the monitoring device.
 13. The system of claim 12, wherein the processing component of each monitoring device is further configured to transmit the estimated location to the remote display through the wireless system.
 14. The system of claim 13, wherein the first user interface comprises a separate field for displaying a location corresponding to each patient wearing the monitoring device.
 15. The system of claim 14, wherein the separate field comprises a map for simultaneously displaying the location corresponding to each patient wearing the monitoring device.
 16. The system of claim 1, wherein the wireless system comprised by each monitoring device further comprises a voice interface to the remote display device.
 17. The system of claim 16, wherein the voice interface operates on a VOIP protocol.
 18. The system of claim 1, wherein the remote device is a computer.
 19. The system of claim 18, wherein the computer is selected from the group consisting of a desktop computer, a portable computer, a tablet computer, a cellular telephone, or a personal digital assistant. 